1. Field of the Invention
This invention relates generally to gyro caging systems and, more particularly, to a passive caging system for use in gyro-stabilized sensor platforms and similar systems.
In the gyro-stabilized sensor platform field, it is essential that the system design adequately protect the delicate instruments of the sensor platform. The gyro-stabilized sensor platform must be protected from excessive shock forces. Currently, such protective measures operate only when the system is powered. In the unpowered state these protective measures are not active and are therefore unable to provide the necessary protection. The present invention provides the required degree of protection while the system is in the unpowered state, without requiring manual intervention or complex system design.
2. Description of Related Art
With gyro-stabilized sensor platforms, motors are frequently employed to actively damp gimbal, and therefore sensor platform, motion. These motors, when powered and active, may enable the gimbal unit to survive shock forces in excess of 20 times the force of gravity. An unfortunate consequence of these motor-damped gimbal systems is their inherent dependence upon power. When power to the motors is shut off, the protection offered by the motors is no longer present. As a result, it is not uncommon for gyro-stabilized gimbal and sensor platform systems to experience failures from shocks and other forces incurred during shipping, handling, and transport by the intended platform vehicle.
Various attempts have been made to prevent shock-related damage and failure of gyro-stabilized gimbal devices while in the unpowered state. A variety of pin-locking devices have been used with partial success. Such pin-locking devices, sometimes controlled by solenoids, serve to lock the inner gimbal frames to the gimbal package when the system is unpowered. These devices have the disadvantage that, through their operation and design, the majority of shock is transferred to the delicate and often expensive inner components, frequently resulting in their damage.
Attempts have been made to incorporate springs or fluid-damped pistons to resolve the problem. Unfortunately, these approaches tend to impair the sensitivity and response time of the gimbal platform. Still other attempts have employed air bladders to protect the gimbal devices. These air bladders frequently require manual intervention of a sensor platform user. They also require that the system design provide an air pump and its attendant electronics.
Fluid dashpots have been used in conjunction with gyro-stabilized platforms to preclude gyro precession angles in excess of design range. By employing linkages between the gyro rotor housing and a fluid dashpot, the disclosed assembly of U.S. Pat. No. 4,193,308 of Stuhler et al. permits unimpeded precession motion over a design range of precession angles while providing caging capabilities to prevent extreme motion states in excess of normal gyro design limits.
U.S. Pat. No. 4,016,960 of Wilcox discloses a dashpot with a guided piston which limits motion of the piston within a cylinder along a particular axis. U.S. Pat. No. 3,939,947 of Cohen, et al. discloses a dashpot for selectively directed damping of applied forces. The dashpot includes a cylinder, a piston which is sealingly slidable within the cylinder, and a piston rod which drives the piston. Various valve members which are connected into the system establish the direction of the damping force.
U.S. Pat. No. 4,322,984 of Lasker et al. discloses a gyroscope caging system having a clamping ring which encircles a portion of the gyro rotor. The clamping ring is adapted to engage an annular groove in the rotor simultaneously with engagement of a groove in a base support member for clamping the rotor during very high acceleration launches of a missile or airborne vehicle. However, it depends upon being actively powered for its operation and cannot perform its clamping function in the absence of power.
U.S. Pat. No. 3,992,955 of Evans et al. discloses a caging mechanism for a gyro in which a flat split ring mounted in a plane perpendicular to the gyro rotor spin axis is deformable to capture the gyro rotor when deformed by a gas activated piston. When the piston is operative, the rotor is either caged or uncaged depending upon the state of the deformable split ring.
U.S. Pat. No. 4,807,485 of Bennett discloses a motor driven caging system for a free gyro which cages both the inner and out gimbals thereof and locks in both the caging and uncaging positions by means of an over-center mechanism. While this system locks in both the caging and uncaging positions, it is not clear what position will be maintained when the system is not powered.
While it is generally recognized that dashpot and linkage systems may provide a damping function to restrict gyro precession beyond design limits, the complex nature of such arrangements increases both material and production costs and adds unnecessary complexity to the system. Further, such damping systems function only while the system is in its powered state. None of the cited prior art discloses the novel features of the present invention which provides gyro platform dampening in the unpowered state.
The present invention provides a passive damping system which operates in the unpowered state of gyro-stabilized platforms and similar systems. Further, the present invention becomes functionally transparent during powered operation of the system. In other words, the damping device is operative only when power to the system is off. Embodiments of the invention may have applications for both closed and open loop gyro systems, as well as in numerous other systems which utilize gimbals to position or isolate delicate instruments and electronics.
In brief, particular arrangements of the present invention involve the provision of a pneumatic caging system for gyro-stabilized sensor platforms. Such gyro-stabilized platforms are frequently employed in the stabilization of certain sensors. One arrangement in accordance with the present invention provides secure caging of an unpowered gyro-stabilized platform through use of a dashpot assembly comprising a pneumatic dashpot in combination with a normally closed solenoid valve. The solenoid is connected to system power. The associated valve is connected in the pneumatic feedback loop. When the system is in its unpowered state, the deactivated solenoid maintains the valve in the closed position. When the piston of the dashpot is confined by the air pressure maintained by the closed solenoid valve, it functions as an equal-force, bidirectional spring. In this manner, effective damping of shock forces is achieved.
When power is applied to the solenoid, the pneumatic valve is opened and unrestricted movement of the dashpot piston is permitted. Accordingly, the gyro-stabilized sensor platform which is connected to the dashpot piston is permitted full and free operation.
The incorporation of a pneumatic dashpot and normally closed solenoid valve design rather than pin-locking devices, springs, fluid-damped pistons, or air bladders, provides effective and inexpensive protection of gyro-stabilized sensor platforms.